Multi-stage magnetic amplifier type of control



y 21, 1959 J. c. MAY 2,896,153

MULTI-STAGE MAGNETIC AMPLIFIER TYPE OF CONTROL Filed April 5. 1955 llllllll!!! I x Jose 077 6, May

ATTORNEYS United States Patent MULTI-STAGE MAGNETIC AMPLIFIER TYPE OF CONTROL Application April 5, 1955, Serial No. 499,379

6 Claims. (Cl. 323-89) This invention relates to electrical controls, and more particularly to controls which utilize saturable reactors and are known as magnetic amplifiers.

The embodiment of the invention illustrated herein comprises a two-stage magnetic amplifier which is utilized to control a lamp load; however, the invention is not limited to the specific embodiment and application shown and described, since it is capable of other embodiments and has distinct utility in connection with the control of electro-responsive devices generally.

An object of the invention is to provide a novel and improved multi-stage magnetic amplifier device with which relatively large loads may be controlled by small input power, said device being characterized by a close regulation, maintaining its various adjusted load voltages substantially constant over a wide range of load values.

Another object of the invention is to provide an improved multi-stage magnetic amplifier as above set forth, which is relatively simple in construction yet has high gain and speed of response.

A further object of the invention is to provide a magnetic amplifier type of control in accordance with the above, which has excellent stability, relatively small voltage drift during warm-up or after extended use, and wherein there are relatively slight deleterious effects due to changes in those components which are subject to aging.

Still another object of the invention is to provide an improved multi-stage magnetic amplifier as above set forth, which is characterized by simple and effective decoupling means between the stages, said decoupling means being non-critical as to its value or action.

A feature of the invention resides in the provision of positive feedback means in a control apparatus of the above type which requires but a relatively small size of current transformer, thus helping to maintain the low cost.

Other features and advantages will hereinafter appear.

In the accompanying drawing the single figure is a schematic circuit diagram of a multi-stage magnetic amplifier type of control made in accordance with the invention.

Referring to the figure, the multi-stage magnetic amplifier control comprises first and second saturable reactors 10 and 11 connected with each other by a coupling circuit 12, said reactors being so arranged and organized as to constitute a pair of magnetic amplifiers for controlling a lamp load 13.

The saturable reactor 10 has a core structure 14, a control winding 15, a damper winding 16, and a pair of load windings 17 and 18 suitably arranged on the core structure 14. The saturable reactor 11 has a control winding 19, a damping winding 20 and a pair of load windings 21 and 22 suitably arranged on its core structure.

The control. winding of the first stage may be connected by leads 23 and '24 to terminals 25, to be energized from a source of direct current, and a resistor-26 may be incorporated in the lead 24 as shown. The damp- "ice ing windings 16 and 20 are connected to each other by wires 27 and 28, with a resistor 29 inserted in the wire 27.

Considering the output side of the circuit, the lamp load 13 is connected by wires 30 and 31 to the end terminals of an autotransformer 32 which has a tap adjacent one end, indicated at 33. One end of the autotransformer 32 is brought to a power supply terminal 34, and one end of the load winding 22 is brought to a second power supply terminal 35. The load windings 22 and 21 are joined by a wire 36, and the remaining end of the load winding 21 is connected by a wire 37 to the primary coil 38 of the current transformer 39, which coil is also connected to the autotransformer tap 32.

It will be understood that, by the above connections, the application of power to the terminals 34 and 35 will cause energization of the lamp load 13, said energization being under the control of the load coils 21 and 22.

The saturable reactor 10 is self-saturating, and to effect this a rectifier network is provided in conjunction with the load coils 17 and 18, as follows: The coils 17 and 18 are connected to each other by a wire 40 which is joined to a power supply terminal 41. The remaining ends of the load windings 17 and 18 are connected by wires 42 and 43 to the ends of the control winding 19 of the second stage, and rectifiers 44 and 45 are inserted in the wires 42 and 43 as shown. A second power supply terminal 46 is connected through rectifiers 47 and 48 with the wires 42 and 43, said wires constituting the coupling circuit 12 between the reactors 10 and 11. A source of alternating current is connected to the terminals 41 and 46, and this may be the same source that is connected to the terminals 35 and 34, thereby to provide load current through all of the load windings 17, 18, 21 and 22, and also to provide the energy for the lamp bank 13.

In the coupling circuit 12 the rectifiers 44, 45 and 47, 48 will cause upwardly-directed pulses in the load windings 17 and 18 of the first amplifier stage and downwardlydirected pulses in the control winding 19 of the second amplifier stage, as shown by the arrows. The control winding 19 will therefore have full-wave rectified current, and the load windings 17 and 18 will each have half-wave current, the latter effecting self-saturation of the reactor 10.

In accordance with the present invention I provide a novel combination of positive and negative feedback means, arranged to energize the control winding 15 of the first amplifier stage to effect close regulation of various adjusted load voltages despite large variations in the load,

thereby enabling various degrees of brightness or dimnessof different numbers of the lamps 13 to be had and maintained at all times. I provide a single positive feedback means comprising the current transformer 39, and a pair of negative feedback means one of which comprises a voltage transformer 50 and the other of which comprises a feedback or coupling resistor 51 interposed in the wire 43 of the coupling circuit 12.

Considering first the positive feedback means, the current transformer 39 has a secondary '52 connected to a rectifier bridge 53 whose output is connected by wires 54 and 5-5 respectively to the wires 23 and 24. Interposed in the wire 55 is a resistor 56.

The voltage transformer 50 comprising the negative feedback means, has a primary 57 connected by wires 58 and 59 respectively to the wires 31 and 30, and has a secondary winding 60 connected to a rectifier bridge 61 whose output is connected by wires 62 and 63 respectively to the wires 54 and 24. Interposed in the wire 63 is a resistor 64.

The drop across the resistor 51 in the coupling circuit 12 is utilized to provide negative feedback, by connecting one end of the resistor, by means of a wire 65, to the wire 54 and by connecting the other end of the resistor 3 t the wire 24 by a lead 66. Interposed in the lead 66 is a resistor 67.

It will be noted that the feedback voltages from the current transformer 39, voltage transformer 59 and drop resistor 51 are all impressed on the single control winding of the first saturable reactor 10. In the'case of the current transformer 39, this enables a much smaller unit to be utilized since the feedback power required of said transformer by the coil 15 is of small magnitude.

In accordance with the present invention I also provide a novel decoupling means in the coupling circuit 12 to efiiect an increase in the gain and speed of response of the apparatus, said decoupling means being relatively simple and non-critical in its value and action. As shown, I shunt the output of the first saturable reactor 10, as brought to the wires 42 and 4 -3 of the coupling circuit 12, with a capacitor 70, and by this organization I provide a path for voltages which are induced in the control winding 19 of the second stage, preventing said voltage from having a deleterious effect on the load windings 17 and 18 of the first stage.

The induced voltages in the control winding 19 in clude harmonics which are also suppressed from the load windings of the first stage, by the capacitor 70. I have found that when the value of the capacitor 70 is increased beyond a certain minimum point, said value becomes non-critical, and that the maximum effect is readily obtained merely by the provision of enough capacity to adequately absorb the said induced voltages. The feedback resistor 51 may also be considered as aiding in the decoupling effect, it being cooperable with the capacitor 70 to effect the desired results of stability, high gain and speed of response. A resistor 72 is shunted across the secondary winding 52 of the current transformer 39, to limit peak voltages when the apparatus is disconnected from or first connected to the power supply for the load 13.

The operation of the circuit shown is as follows: With a minimum amount of D.C. control voltage on the terminals 25, and with the terminals 34, 35 and 41, 4:6 energized from a source of A.C the lamp bank 13 will be at its dimmest, due to most of the load voltage being absorbed by the load coils 21 and 22 of the sec- .ond amplifier stage. Such absorption occurs because there is a minimum of D.C. control energy in the control winding 19 of the second stage as a consequence of most of the voltage for said winding being absorbed by the load windings 17 and 1 8 of the first stage. Such ab- ,sorbing of voltage in the first stage is made possible due toi th e control winding 15 thereof having minimum current As the D.C. control voltage across the terminals 25 is increased it will provide a greater energization of the control winding 15, resulting in the producing of flux in the core structure '14 of the first saturable reactor. This will prevent the load windings 17 and 18 of the first reactor from absorbing asmuch of. the voltage as they previously did, and therefore more voltage will be available to the control coil 19 of the second reactor 11. As more voltage is applied to the control winding 19 it will produce flux in the core of the reactor 11 and prevent the load windings 21 and 22 thereof from absorbing as much voltage as previously; accordingly more of the voltage applied to the terminals 34 and 35 will be made available to the autotransformer 32, causing a greater energization of the lamps 13 and more brilliance. In this manner the lamps 13 may be made either bright or dim, or else made to have varying degrees of brightness, and for each setting of the apparatus the particular energizing voltage applied to the lamps will be maintained constant, regardless of changes in the lamp load. Thus, if the lamps are being operated at one-half brilliance they will show this same brilliance even though some lamps are removed or others added.

The control apparatus of the present invention is relatively simple, effective in its operation, and reliable over an extended period of use regardless of aging of components. No moving parts are involved that might get out of order, and the operation is characterized by a close regulation, quick speed of response, and relatively high gain. As a consequence of the latter it is necessary to apply only a small amount of power to the terminals 25 to control a much larger amount of power supplied to the terminals 34, 35 and 41, 46. By the provision of the resistor 72, peak voltages which might occur in the secondary 52 of the current transformer 39 will be greatly reduced and prevented from causing damage to the rectifier bridge 53.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

I claim:

1. A multi-stage magnetic amplifier comprising a pair of saturable reactor devices and a coupling circuit therefor, said devices having magnetic core structures and load and control windings on said core structures, the load winding of one of said' devices and the control winding of the other device being connected in said coupling circuit; a supply circuit connected to said load winding; rectifier means in said circuits, providing for unidirectional energization of the control winding when the supply circuit is energized with A.C., said unidirectional energization being under the control of said load windings; a load circuit connected to the load winding of the other saturable reactor device; means for feeding a portion of said unidirectional energization to the control winding of said one reactor device; means responsive to current in said load circuit, providing for an energization of the control winding of said one saturable reactor; and means responsive to the voltage of said load circuit, providing for an energization of the control winding of said one reactor device,

2. The invention as defined in claim 1 in which there are means associated with said feedback means, providing a relationship between the same to cause the load voltage to remain substantially constant regardless of changes in the load.

3. The invention as defined in claim 1 in which the means for feeding a portion of the unidirectional energization comprises a resistor in the coupling circuit, and comprises connections to utilize the voltage drop across said resistor.

4. A multi-stage magnetic amplifier comprising a pair of saturable reactor devices and a coupling circuit therefor, said devices having magnetic core structures and load and control windings on said core structures, the load winding of one of said devices and the control winding of the other device being connected in said coupling circuit; a supply circuit connected to said load winding; rectifier means in said circuits, providing for unidireo tional energization of the control winding when the supply circuit is energized with AC, said unidirectional energization being under the control of said load winding; a load circuit connected to the load winding of theother saturable reactor device; means for feeding a portion of said unidirectional energization to the control winding of said one reactor device; means responsive to current in said load circuit, providing for an energization of the control winding of said one saturable reactor; means responsive to the voltage of said load circuit, providing for an energization of the control winding of said one reactor :device; and means connected to said coupling circuit,- providing a low reactance path for harmonic pulses induced in the. control winding of the other of said devices, to minimize the likelihood of said pulses passing through the load winding ofsaid one device.

5. The invention as defined in claim 4 in which the means for feeding a portion of said unidirectional energization. to the control, winding includes a resistor conneetedin the 7 coupling circuit between thecontrol winding and the means providing the low reactance path for harmonic pulses.

6. A multi-stage magnetic amplifier comprising a pair of saturable reactor devices and a coupling circuit therefor, said devices having magnetic core structures and load and control windings on said core structures, the load winding of one of said devices and the control winding of the other device being connected in said coupling circuit; a supply circuit connected to said load winding; rectifier means in said circuits, providing for unidirectional energization of the control Winding when the supply circuit is energized with AC, said unidirectional energize.- tion being under the control of said load winding; means connected to said coupling circuit, providing captive reactance across the leads supplying current to the said control winding, to minimize loss of gain; and a damping UNITED STATES PATENTS 2,518,865 Cartotto Aug. 15, 1950 2,555,992 Ogle June 5, 1951 2,651,155 Ogle Oct. 21, 1952 2,717,346 Geyger Sept. 6, 1955 2,735,053 Storey et a1 Feb. 14, 1956 OTHER REFERENCES Publication: Flux Preset High-Speed Magnetic Amplifiers, by C. B. House, AIEE Transactions, v01. 72, January 1954; pages 7 31-732. 

